The present invention relates to an ink-jet recording sheet and a liquid coating composition for forming a recording layer to prepare an ink-jet recording sheet. More particularly, the invention relates to a liquid coating composition suitable for forming, on the surface of a substrate sheet, an ink-receptive layer for ink-jet recording having high water resistance, excellent transparency, good ink absorptivity and good color developability as well as little stickiness not to cause a disadvantageous phenomenon of blocking of sheets.
It is a widely practiced convenient procedure in recent years to prepare posters and other printed materials for presentation by printing out patterns and images formed and stored in computer memories by utilizing a printer operated by the computer along with increasing prevalence of the computer technologies. The printers employed in these technologies include dot-impact printers, laser printers, thermal printers, ink-jet printers and the like, of which ink-jet printers and ink-jet plotters are most widely employed because these machines have advantages that printing-out can be performed with little machine noise, printing-out in full color can be performed therewith and the running cost for printing out is low.
The paper sheet used in printing in an ink-jet printer or ink-jet plotter can be a sheet of plain paper or coated paper but, besides, a recording sheet which is a plastic film provided with an ink-receptive layer on at least one surface of a substrate can also be used. Recording sheets of this type are widely used in the preparation of posters having colored images because the printed material obtained by printing out on such a recording sheet is excellent in the gloss of the surface. The paper size required in such printing is increasing to reach the A3 to A0 size to exceed the A4 size most widely used in the preparation of general documents.
Various coating compositions have been proposed heretofore for forming such an ink-receptive layer on a substrate to prepare an ink-jet recording sheet. For example, Japanese Patent Publication 6-427 proposes a coating composition comprising a polyvinyl alcohol and polyvinylpyrrolidone. Japanese Patent Kokai 7-40646 discloses a double-coated ink-jet recording sheet of which the undercoating layer contains a polyvinylpyrrolidone and the overcoating layer contains a polyvinyl alcohol. Due to the hydrophilicity of these polymers, however, the ink-receptive layer has low water-resistance so that use of the recording sheets outdoors or under a highly humid atmosphere is limited along with a disadvantage of blocking of the sheets stacked one on the other.
Various proposals have been made with an object to overcome the above described problems and disadvantages of the ink-jet recording sheets in the prior art. For example, Japanese Patent Kokai 61-188183 discloses an ink-jet recording sheet having an overall linear transmittance of at least 30%, of which the ink-receptive layer contains from 5 to 50% by weight of colloidal silica particles having a particle diameter not exceeding 80 nm. Japanese Patent Kokai 63-178173 proposes a substrate of an ink-jet recording sheet which is a film of a polyvinyl alcohol modified with acetoacetyl groups and admixed with an organic adjuvant compound selected from aldehyde compounds, amine compounds and epoxy compounds.
The above described ink-jet recording sheets have respective defects in several respects. Namely, the ink-receptive layer containing colloidal silica particles is defective in the low water resistance because the resinous ingredient forming the ink-receptive layer is a water-soluble resin such as polyvinyl alcohol and polyvinylpyrrolidone. The ink-jet recording sheet having an ink-receptive layer based on a substrate of an acetoacetyl-modified polyvinyl alcohol containing an organic adjuvant compound is defective because of the low ink receptivity as well as poor pattern reproducibility and color development.